Maintaining viewstate of a repeater

Question

I have a problem whereby the viewstate of a repeater i.e. the controls within the repeater are not maintaing their viewstate.

I have the following:

Repeater 1:

<asp:Repeater ID="rptImages" runat="server">
<ItemTemplate>
    <asp:LinkButton Text="Add" CommandName="Add" CommandArgument=<%# Eval("ID") %> runat="server" />
</ItemTemplate>
</asp:Repeater>

When the link button is clicked the value of the CommandArgument is stored in a hidden field on the page.

Upon postback I can't get the value of the hidden field until the prerender event handler has loaded. So in my prerender event I grab the value of the hidden field and store it in a List property, like so:

if (!string.IsNullOrEmpty(this.SelectedImageIDsInput.Text)) {
        this.ImageList.Add(this.SelectedImageIDsInput.Text);
    }

And the List property looks like so:

public List<string> ImageList {
    get {
        if (this.ViewState["ImageList"] == null) {
            this.ViewState["ImageList"] = new List<string>();
        }
        return (List<string>)(this.ViewState["ImageList"]);
    }
    set { this.ViewState["ImageString"] = value; }
}

Once I have stored the value into my List property I bind my second repeater (again within the prerender event):

this.rptSelectedImages.DataSource = this.LightBoxControl.ImageList;
this.rptSelectedImages.DataBind();

The second repeater has a dropdownlist and a textbox within it. The problem is that the viewstate of these child controls is not maintained. I presume it is because with each postback I am rebinding the repeater, therefore it is rebuilt. What I don't know is how I can possibly get round this? The ImageList property is only updated upon a postback, so I obviously have to rebind the repeater with each postback - how else can it be done?

Any help would be greatly appreciated.

Thanks Al